Quantitative measurement of serum alphafetoprotein (AFP) has been used to monitor various neoplastic diseases and has been shown to correlate with the clinical course. It becomes even of greater value when used in conjunction with other known tumor markers, i.e. hCG and CEA. Studies of catabolism and synthesis of AFP are in progress to relate serum AFP levels to actual number of tumor cells. Studies of an antigen associated with human lung carcinoma have concentrated on isolation of the antigen by various methods, development of new antisera, and providing a quantitative assay for the antigen. The most efficient method for isolation of this suspected cytoplasmic antigen now includes the treatment with acid (pH 1), chromatography on DEAE and then electrophoretic separation on polyacrylamide gel. A quantitative electroimmunodiffusion method for measurement of the antigen was developed, but was relatively insensitive, being able to detect a lower limit of 1.5 micrograms/ml. A method of immunologic staining using horseradish peroxidase has demonstrated the antigen in 28 of 28 formalin-fixed lung tumors, but in none of 4 normal lungs. The antigen is also found in adenocarcinomas of the colon and pancreas.